Lesslie Newbigin was a British theologian, missiologist, missionary and author. Though originally ordained within the Church of Scotland, Newbigin spent much of his career serving as a missionary in India and became affiliated with the Church of South India and the United Reformed Church, becoming one of the Church of South India's first bishops. A prolific author who wrote on a wide range of theological topics, Newbigin is best known for his contributions to missiology and ecclesiology.

Walter Rauschenbusch (1861–1918) was a Christian theologian and Baptist pastor who taught at the Rochester Theological Seminary. Rauschenbusch was a key figure in the Social Gospel and 'Single Tax' movements that flourished in the United States during the late 19th and early 20th centuries.